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Old 10-23-2007, 04:32 PM   #1
MasterKwan
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Default Boost overshooting target.

I've been seeing my boost overshoot target and then oscillate once or twice before it settles on target boost. I've logged it and see the higher than target boost and the correction by the ECU to the duty cycle. Essentially it looks like the steps are too big so, it has to hunt a little for target boost.

I had jerked with the waste gate arm (shortened it) but believe I've put it back to stock. What I was thinking is that I could tone down the continuous turbo dynamic table to both slow the buildup of boost and reduce the undershoot.

I notice on the JDM WRX ECU for 03, the continuous table is symetric around 0 boost error but, the US table corrects more in the negative than the positive.

Boost Error
-0.20 -0.11 -0.05 -0.02 0 0.02 0.05 0.11 0.20

US
-5 -4 -3 -1 0 0.19 0.39 1 3.13

JDM
-3.13 -1 -0.39 -0.19 0 0.19 0.39 1 3.13

I was toying with the idea of using the JDM table and perhaps reducing the max delta duty cycle to 2.5 on either end.

Any suggestions? And yes, I might have to loosen the actuator another 1/2 turn but, so far changing the actuator hasn't changed the symptoms.
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Old 10-23-2007, 06:27 PM   #2
Broxma
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I should make a little primer on how to tune WGDC and Burst/Continuous tables to achieve solid boost.

Drop the WGDC at the RPM you see the boost error go into the negative or adjust the continuous on the negative side. .

Remember, when your on throttle, total WGDC is base+continuous based on error, but negative means too much boost.

I'd have to see a log and what your tables are set at.

/Brox
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Old 10-23-2007, 08:28 PM   #3
MasterKwan
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Thanks for the comments.

The tables are currently stock for my 03 WRX. I have:

TD04
Catless up,
STI TMIC
K&N Panel filter
TGV Deletes

I'm overboosting at about 60-61 WGDC. It settles to target boost (13.61) about 55 WGDC according to the logs. The stock map has max WGDC at 69 for the same RPM and throttle angle. I was toying with the idea of reducing WGDC MAX to something like 57 to cap off the boost. I just wasn't sure that was the best way to do it. I was assuming the stock MAX WGDC of 69 was that way for a reason.

Seems like I can attack this more than one way, cap off the MAX WGDC or slow down the rate of increase in WGDC so, it doesn't overshoot target boost.

I'm a tuning Noob but, I've been on a crash course of reading over a Enginuity.
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Old 10-23-2007, 11:09 PM   #4
Freon
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If it is a fast oscillation (1+ hz) , lower your proportional map values. If it is a slow oscillation (<0.5 hz), lower the integral.

Some of the JDM ecus have the newer boost control scheme found in the later 2.5L US cars so the maps are not really comparable. If that JDM ECU has an initial duty map then it has the newer style boost controller, and I would not recommend using its turbo dynamics maps.
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Old 10-24-2007, 12:06 AM   #5
Broxma
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I tuned for target boost with my Perrin EBCS by dropping WGDC about 75% across the board and then raising it in 5% increments. I also cut the cont/Burst maps in half.

Once I hit target at WOT, I started cutting more from the cont/burst map until I started to overshoot, then put them back to the previous setting.

Then I started doing 75% and 50% throttle incremental increases. These are the ones I noticed most.

The large boost over shot I have seen has always been to much initial WGDC and not enough negative continuous, or too little or adequate WGDC and too much positive. Theres a few variables there but Sounds like you can figure it out.

/Brox
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Old 10-24-2007, 12:43 AM   #6
MasterKwan
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Looks like a 2-3 second oscillation. Probably closer to 2. The burst table kicks in in one sample time but, most of the correction's happening from the continuous table.

I assume "integral" = "continuous".

Is there any reason the max WGDC should be significantly higher, 15 units than my observed WDGC for target boost?

Thanks.
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Old 10-24-2007, 02:24 AM   #7
Broxma
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Not unless the Continuous table is set really high.

I downloaded a map from OSECU, not one of theirs but a Open tune from a random post, where the guy had set the highest boost error correction to something like 40.00.
I imagine boost would come on strong but overshoot like crazy. I didn't actually flash and run the map, was just looking at it.

Check your Continuous tables and see what they are set at. The Stock BC sometimes needs a fairly large correction. I don't know about 40, but...

/Brox
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Old 10-24-2007, 08:57 AM   #8
MasterKwan
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Yeah, after lots of research, I'm steering clear of the OSECU roms other than as examples. Since I primarily track the car, I need to keep it on the conservative side.

I'm a bit disturbed because I see injector duty cycles in the 95% range even though I consider my mods to be minimal at best.

I cut back the continuous a bit to make it ramp boost up slower and hopefully not overshoot as much. If that doesn't work I'm going to reduce the max WGDC to perhaps 10 less than current for the RPM's and throttle positions where's it's currently 69.

Just to be clear, other than some minor tweeks to the cold start and OL/CL delays, this is a stock WRX ROM.
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Old 10-24-2007, 11:22 PM   #9
MasterKwan
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Ok, this seems to have done it. I'm getting boost errors under .5 PSI now...most of the time. I'm not seeing the negative corrections I was seeing before. I may step it up a touch till I get to the point it starts overshooting.

One thing I notice is that the negative corrections are very aggressive. I may flatten them out some too.
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